1. Field of the Invention
The present invention relates to a digital TV antenna and in particular to a digital TV antenna structure having switchable multiple bandwidths.
2. Description of Prior Art
Conventionally, picture signals of a common household television (referred to as an analog TV) changes continuously and adopts a NTSC system. On the contrary, in a digital television, the picture signals are subjected to a digital processing to become a series of data. Then, the thus-formed data are subjected to a digital modulation and transmitted to a digital box or a digital television in the house, so that digital television programs can be watched.
The progress of video compression technology facilitates the success in the digital television. The current international standard of compression is MPEG-2. In the television channels of a conventional wireless television having a bandwidth of 6 MHz, 1080 horizontally scanning lines can be transmitted. Such a high definition television is referred to as a HDTV. In comparison with the traditional television having 525 scanning lines, the picture of the HDTV is fine and delicate, and the color thereof is vivid. Further, the HDTV can provide a stereo, high-class Dolby AC3 audio effect.
In recent years, with the continuous progress of technology, many electronic products tend to be light and compact whereby a user can carry them to the outside very easily. Therefore, the volume of the digital television is also reduced to become a portable mobile digital television. As a result, the user can carry it to the outside or mount it in a car. When using a portable digital television to watch programs, it is necessary for the user to connect an external antenna to the housing of the digital television. With this antenna receiving signals, the user can watch digital television programs in a car or in the outside. In order to increase the range of frequency bandwidth that can be received by the digital television, the dimension of the digital TV antenna is always made larger, such as those disclosed in Taiwan Patent Publications No. M277120 (FIG. 1), No. M279994 (FIG. 2), No. M284146 (FIG. 3) and No. M286443 (FIG. 4). As a result, the digital antenna can be only connected externally to the digital television but cannot be built in the portable digital television. Therefore, it is very inconvenient for the user to carry such a large digital antenna.